Hydraulic actuating apparatus



Feb- 16, 1960 r-:.-J. svENsoN 2,924,939

- V HYDRAULIC ACTUATING APPARATUS Filed Dec. 2o, 1954 s sheets-sheet 1 Feb-16 1960 E. J. SYENSON v 2,924,939

HYDRAULIC ACTUATING APPARATUS y y Filed Dec. 20,1954 6 Sheets-Sheet 2 Feb. 16', 1960 Filed Dec. 20, 1954 E. J. SVENSON HYDRAULIC ACTUATING APPARATUS e sheets-sheet s Feb.' 16, 1960 E. J. svENsoN 2,9?4939A I f I HYDRAULIC ACTUATING APPARATUS I Filed Dec. zo, 1954 e sheets-sheet 4j 425;: ff-4 '404- f. .ag 416 T IN VEN TOR. p 405 Erfze fyemsan Feb. 16, 1960 E. J. SVENsQ-N 2,924,939 Y HYDRAULIC ACTUATING APPARATUS Filed Dec. 20, 1954 6 Sheets-Sheet 5 Fab. 16, 1960 E. J. svENsoN 2,924,939

HYDRAULIC ACTUATING APPARATUS Filed vec. 2o, 1954 6 sheets-sheet s IN VEN TOR.

.fracy to obtain the desired results. shiftable element of the machine carries a` tool or a 2,924,939 HYDRAULIC ACTUATING APPARATUS Ernest Svenson, Rockford, Ill.

Application December 20, 1954, Serial No. 476,281

8 Claims. (Cl. 60-52) workpiece, it is necessary that theshiftable element be moved .in fa predetermined manner and with great accuracy so that' the workpiece willbe provided with the desired dimensionsor finish. It will be apparent that in such machines; it-isnecessary to stop the shiftablel element at the end ofthefeeding motionwith great accuracy and inmachinesheretofore in use, whether incorpera-ting mechanical or hydraulic feeding mechanisms, it has generally been. necessary to provide a mechanical ypositive stop for limitingthe movement of the shiftab'leV `element `in order toobtain the desired accuracy. One V reason for this when a: hydraulic actuatnig mechanism is used is that thehydraulicA fluid compresses, slightly when placed under actuating pressure.V For example, the United States Bureau of. Standards `gives the compressibilit-y of a fluid such as turbine oil which is common-ly, used in actuating systems as approximately one-half of one percent when the pressure is raised from one to one thousand p.s.i. This compressibility ofthe hydraulic fluid not only precludes. fgreataccuracy in stopping of lthe actuator element. of many structures heretofore in use without the aid of a mechanical stop, but also may cause the movement of the hydraul-ically actuated member to be uneven. More specifically, when the ilu-id is rst placed'under pressure the shiftable element or piston will remain substantially stationary until the fluid has been compressed whereupon the piston will jump forwardly,

,then slow down or stop as the lluid expands whereupon the tluiclk will -again be compressed and the piston will again jump forwardly. While these effects resulting fromthe compressibility of the hydraulic fluid are not unduly objectionable in manyof the machine heretofore in use, there are instances when it is desirable to move the shiftable element or piston at an extremely uniform rate and tostop the piston-or shiftable element with an extreme degree of accuracy.` It is,lth'erefore, an important object of the present Yinvention to provide a novel hydraulic actuating apparatus wherein the effect of the compressibility of the hydraulic lluid is substantially eliminated.

A more specicobject of the present invention is to provide a novel vhydraulic actuating apparatus which is' constructed so that the shiftable element'or piston thereof may be` stopped with athigh `degree of accuracy. lIn accordance with the Vpre-sent invention, a hydraulicactuating apparatus may ybe constructed so that the actuated member or piston .may be stopped within .00001 (one hundred-thousandth) ofan inch or less.

Another objectof the prese-nt invention is to provide i a novel hydraulic actuatingrapparatu's 'of the Iabove described typezwh'ereinfthe'actuated linember or piston-may Urli@ Sta-frs Para@ C 2 b e stopped with a high degree of accuracy at various times and at various positions without the -aid of a positive mechanical stop Still another` object of the present invention is to pro- 5 vide a-novel hydraulic actuating apparatus which is constructed so that the actuated member or piston may be startedand moved at' an extremely uniform rate.

A further object of the present invention is to provide a novel hydraulic actuating mechanism of the above described type which is constructed so that the actuated member or piston may not only `be shifted at a substantiallyuniform rate but may also be shifted -at a slow rate which may be on the order of .001 (one ten-thousandth) of an inch per second whereby the total distance which -theactuated member o-r piston is fed may be determined -by a timer, if desired.

Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings wherein:

Fig. l is a diagrammatic view illustrating a novel hydraulic actuating apparatusfembodying the principles of this invention;

Fig. Zis an elevational view,partially broken away,

showing apumpy assembly incorporated inthe apparatus `showing another two-position four-way directional con- Y trol valveutilized in the apparatus;

Fig. 6 isa sectional view showing a relief valve utilized in the apparatus;

Fig. 7 is a `section-al view showing a check valve utilized in the apparatus;

Fig. 8 is a sectional view showing a manually adjustable lby-pass valve incorporated into the apparatus of this invention;

Fig. 9 is an elevational view partially broken away, showing a three-position four-way directional control valve utilized in the apparatus;

Fig. l0 is a sectional view of a manually operated ball seat reset valve utilized in a modied form of the present invention; and t Fig. ll is a diagrammatic view showing a novel hydraulic actuating apparatus embodying a modied form of the present invention.

Referring now more specifically to the drawings wherein like parts are designated by the same numerals throughout the various figures, an apparatus 2i) incorporating the principles of this invention is diagrammatically shown in Fig. l. In general, this apparatus includes a reservoir 22 for hydraulic fluid, a feed pump assembly 24 including a gear pump 26 and a plunger type pump 28, a rapid traverse pump 30, a pair of iiuid motors 32 and 34, a two-position four-way control valve 36, a plurality of two-position four-way control valves 38, 40 and 42,'a three-position four-way directional control valve 44, a pair of check valves 46 and 48, a relief valve 50, anotherY relief valve 52, and `a manually adjustable by pass valve 54.

The gear pump 26 of the feed pump assembly 24 which is shown in Figs. l and 2 may be vof known construction and, therefore, need not be described in detail. n It suffices to state'that the gear pump is continuously driven and deliversV compressed hydraulic fluid under pressure for charging the plunger pumpZS. While hydraulic fluids or liquids are generally thought to be incompressible by -locked in any adjusted position by nut means 100.

by the plunger pump back to the inlet side of the gear t pump.

The plunger or piston pump 28 is adapted to be charged with the compressed hydraulic iluid under pressure from the gear pump and then to deliver a metered amount of compressed hydraulic uid under pressure for actuating the uid motors. The piston pump is provided with a plurality of piston chambers indicated at 58, 60 and 62 in Fig. 1, and a piston or plunger 64 is disposed in each of these chambers. The piston-chambers are charged pump shown and described in my copending application and the pistons are forcedinwardly by the'uid underV y port 138 of the relief valve and the reservoir.

having an outer race 78 and an eccentric inner race 80X One end of a pivotally mounted lever 82 is disposed between the outer race 78 and an associated plunger or` piston 64 so that as'the lever is shifted by the eccentrically mounted and formed bearing assembly which rotates with the shaft 66, its associated plunger is recprocated.

In order to adjust the length of the piston strokes and therebyV adjust the volume of hydraulic duid which is metered through the plunger pump, adjustable means is provided for limiting the inward movement of each of the levers 82 and, therefore, the inward movement of each'y of the pistons. This adjustable means includesa gear 84 rotatably mounted in the pump housing and having a A plurality of cam portions 86, each projecting for cooperation with a finger or extension 88 of one of thelevers 82. The cam portions 86 are formed so that by rotating the gear 84 inward movement of the levers and pistons is adjusted. In order to rotate the gear 84 and thereby adjust the cam portions 86, a pinion 90 meshes with the gear 84 and is fixed on a shaft 92 rotatably mounted in the pump body 74. The shaf-t 92 is coupled with a shafty 94 as at 96, which, shaft 94 extends through an end plate 98 secured to the pump housing. Thus, upon rotation of the shaft 94 the pinion 90 rotates to adjust the gear 84. The shaft 94 and, therefore, the gear 84 may be In ordervto drive the gear pump 26, the shaft 66 is p-rovided with an extension 102 which is coupled as at 104 with a drive shaft of the gear pump. As will be understood, the plunger pump is provided with suitable passageways and check valves in the body 74 for directing charging iluid from the gear pump into the piston chambers and for directing the uid from `the piston chambers to the outletl of the pump. In accordance with the present invention it is important to note that the relief valve 56 of the gear pump is set so that the pressure of the charg-y ing fluid directed from the gear pump to the piston pump is only slightly less than the pressure of the fluid delivered by the piston pump. With this arrangement the hydraulic fluid is already compressed substantially the same amount when it enters the piston pump as'when it leaves the pump so that the effect of the compressibility of the hydraulic fluid has been substantially eliminated within the pump. While the piston pump is only briey shown and described hereinl certain structural details thereof such as the internalv passageways, check valves, *l

plungers, levers and eccentric actuating means are essentially the same as the corresponding elements of ya piston Serial No. 437,067, filed June 16, 1954, to which appli-- cation reference is hereby made to complete the disclosure relative to the piston pump.

As shown in Fig. 1 the gear pump 26 is provided with an inlet 106 which is connected with the reservoir by a conduit 108. The gear pump outlet 110 is connected with the feed pump or piston pump inlet 112 through the valve 36. More specifically, the conduit 114 extends between'the gear pump outlet and an inlet port 116 formed in the body 118 of the valve 36 and -a conduit 120 extends between the inlet port 112 of the piston pump and an outlet port 122 of the valve. As shown best in Fig. 5, the valve36 includes a valve stem 124 slidably disposed in a central bore 126, which bore is intersected by the ports 116 and 122. The valve body 118 is also provided with a drainport 128 ywhich is connected with the reservoir through the relief valve 52- by conduits 130 and 132 which communicate with the inlet port 134 of the relief 4valve and conduit 136 which extendsl between the outlet The valve stem 124 is normally resiliently biased to Vthe `position shown in Fig. 5 by a compression spring y140. In this position it is seen that the inlet port 116 is blocked from the outlet port 122 and thus, from the piston pump by a valve stem portion 142. At the same time, the inlet port 116 communicates with the drain yport 128 along the reduced diameter portion 144 of the valve stem. When it is desired to actuate the uid motors, the valve stem 124 is shifted toward the left as viewed in Fig. 5 so that communication-between the inlet port 116 andthe drain port 128 is broken by the valve'stem portion 146 andthe charging uid may ow from the inlet port 116 alongV the reduced diameter por- 35.

jshift the lvalve stem against the action of the spring tion 144 and through the outlet port 122. In order to the valve is provided'with a solenoid 148 having shiftable member'150 which actuates'the valvev stem through a pivotallymounted lever 152.

Whenk the valve stem 1 24 is shifted from the neutral or stop position shown in Fig. 5 to theY start position,

' charging fluid from the gear'pump enters the piston pump and the piston pump meters and delivers a predetermined metered volume of fluid at a predetermined rate through its output port 154. The outlet port is connected with a conduit 156 which, in turn, is connected with a conduit 158. One end of the .conduit 158 is connected with the normally closed safety relief valve 50 which, in turn, is connected with the reservoir by a conduit 160. The relief valve 50 functions to direct the Vuid back to the reservoir in the event the pressure in the line 158 becomes unduly high. However, when the valves and the uid motors are functioning properly and the fluid motors are not overloaded, the relief valve will remain closed and the fluid will be directed through the conduit 158 to the inlet port 162 of the valve 38.

vAs shown in Figs. 1 and 4, the valve 38 includes a body member 164 having a central bore 166 in which a valve stem 168 is slidably disposed. The inlet port 162 intersects the bore, and the valve body is `also provided with outlet ports 170 and 172 which communicate with the bore. With theV valve stem 168 in the position shown in Fig. 4, the hydraulic fluidl flows from the inlet port 162`along ja reduced diameter portion 174 and into the outlet port 170. As is fully described below, the fluid is directed from the outlet port 170 so as to actuate the uid motor 32 and in order to actuate the fluid motor 34,`the valve stem 168 is shifted toward the left as viewed `inFig. 4 so as to direct the fluid from the inlet port 162 y.174 and 176, respectively, including. shiftable members annessa and180. '[fheshiftable members actuate the valve stem through afpivotally f mounted. lever 182.

When V'it is desired 'to` actuate. or feedthe shiftable element of theuid motor 32,-the4 valvefstem 168is located 1in the position shown in Fig. 'ilso'V that. the compressed hydraulic uid from the .pistonpump is directed through 'the outlet port 170,"into a conduit- 184connected therewith. .The conduit 184 is connectedl with an 4inlet 186 of the check valve 46, which check valve is shown in detail in Fig. 7. The check valve 46 includes a tubular body member 188 having opposite-ends closed by plugs 190 and 192 which respectively provide the inlet opening 186 and an outlet opening 194. .At the inner end-of the plug V190 there is provided a valve 'seatY 196 against which a uted valve member 198 is resiliently urged by a compression spring 200. As will be understood, the hydraulic ilui'd Vunder pressure from the piston pump unseats the lil'ute'd valve member 198 so that the uid may ow through the check valve and the outlet ,opening 194 into aconduit 202. The conduit .202 'joins a conduit 204 which has one'end connected with an inlet port 206 of the valve 40 and an opposite end connected with the valve 44. When the Huid motor 32 is to be actuated by the fluidfrom the piston pump, the valve 44 is positioned so as to block the associated end of the conduit 204 in the manner described below so that the nid flows through the conduit 204 and into the port 206 of the l'valve 40. As shownl in Fig. 3 the valve 40 includes a body member 208 having a central bore 210 which is 'intersected'by the inlet port 206 and in which a valve 'stem 212 is slidably disposed. The body member is also `pro'videdwith outlet ports 214 and216 which communicate with the central bore. In addition, the body lmember 208 is provided with ports V218and 220 which comjmunicate with the central'bore. The ports 214 and 216 are respectively/'connected with opposite ends of the uid motor 32 by conduits 222 and 224, and the ports 218 and 220 are connected` with the inlet of the relief valve 52 by conduits 226 and 228respectively, which conduits in turn are connected with a conduit 230 that joins the above described conduit 132. With the valve stem 212'in the position shown in Fig. 3 it is seen that communication is established between the inlet port 286 fand the .outlet port 214 by a reduced diameter portion stem and 'out through the .port 220 from where it is directed through the relief valve 52. In' order to actuate 'the fluid motor 32 in the opposite direction, the valve stem 212 is 'shifted toward the left as viewed in Fig. 3

jso that communication between the ports 206 and 216 'his established. In addition, the valve stem portion 236 interrupts the passageway between the ports '216 and 228 'and the valve stem portion 234 is shifted so that uid rna'yllow between the ports 214 and -218 arounda reduced diameter portion 240` of the valve stern. When the' valve stem 212 is shifted toward the left `as just described, the uid ows from the inlet port 206 through the port 216 vandthe conduit 224 to the upper end of the fluid motor, and fluid from the lower end of the motor returns through the conduit 222 into the port 214 from where it ilows tothe port 218 and. through the conduit .i226 and connecting conduits to the. relief .valve 52. In l"order to shift the valve stem 212 the valve40 is provided with "a jp'air of solenoids 242 and 244, respectively, in-

fjcluding shiftable members 246. and 24Sjvvhich actuate the 'valve stem through a pivota'lly,v 'mounted lever or fance 'with thefipres'e'ntfinventiom theuuidf motor 32 Vshown 'for purposesr Iof illustration includes a hydraulic cylinderV 252 f and""a double-ting piston 254 slidably disposed'within.thecylinderv O'n'e end of the cylinder is closed .and sealed by 'suitable means 256 and a ram 258 is Xe'd to t-hepiston andeXt'ends through suitable means 260 closing andsubstantially sealing the opposite end of the cylinder. `The Apiston and ram are formed so Vthat there will be predetermined frictional resistance to relative sliding motion between them and the cylinder. By way 'offeXample only, this frictional resistance which is utilized-in the'r'nanner described below may be s 'uchl as Vto require the application of fluid under a pressure Aof "four to five p.s.i. to the piston in order to obtain relative sliding movement between the piston and lthe cylinder. y i

The relief valve 52 whichis `shown in Figs. 1 and 6 includes a body member 262 having a central bore 264 which communicates with'the outlet conduit 136. An Y auxiliary body member 266 having the inlet opening 134 therein is threadedinto the bodyfmember 262. The body member 266 is provided with a central bore 268 which slidably receives a valve member 270. The valve member has an uninterruptedfpontion 272 which serves to block the bore 268, and an annular groove `274 disposed at an angle to the axis ofthe Vvalve member, and one or more groovesf2'76fr establishing communication between the inlet opening` 134 and the annular groove 274. The valve member is resiliently biased to the position shown in Fig.6 by a compression spring 278 which acts against an adjustable plug 280 threaded into the body member 2F62.- As lwill be understood, the pressure at which the valve -memberQ270 will be open maybe adjusted by turning the plug 280 to vary the back pressure applied. bythe. spring`278. In orderA to promote smooth operation of :the relief valve, the annular groove 274 is inclined asdescribed above so that as the valve opens and the grooveemerges from the bore 268, the effective size of the valve. opening or iluid passageway will increase or vary progressively rather than abruptly. Gradual opening yand closing of the relief valve is also promoted by providing the body member 266 with a counterbore 282. u

In accordance with the present invention, the apparatus thus far described is adjusted and operated as follows. The piston feed pump is', o'f course, ladjusted to deliver a needed volumeof compressed hydraulic fluid at a desired rate and at a desiredpressure, and the .gear pump relief valve 56 is adjusted so that the gear pump delivers charging iluid at a pressure only slightly below the pressure of the uid delivered by the Afeed pump. By way of example only, it may be stated that the feed pump can be adjusted to deliver hydraulic Vfluid at a rate which will cause actuation or shifting ofthe fluid motor piston very slowly a-tabout .0001 of an inchper second. In addition, the relief valve 52 is adjusted so as toprovide a substantial back pressure in .the fluid motor 32. This back pressure should be such that when added to the resistance or back pressure Vprovidedby the friction between the piston and the cylinder and the load applied to the ram, the total back pressure on the piston-is suflicient to maintain the compressed actuating hydraulic fluid from the feed pump. in a substantially uniform state of compression while, of course, permitting shifting or actuation of the piston.V In thismanneL-surging or irregular motion of the piston is substantially eliminated and the piston may be actuated at a highly uniform rate of speed. When determining therback pressure to be provided by the relief valve 52, the difference in the areas at the opposite sides or ends .of-the. piston as a result of the ram must be considered. In certain instances when the smaller end of lthe pistoni-is very small as compared with the area of the larger piston end, it may be desirable to connect the conduits 226 and 228^with gozaban lseparate relief valvesratherthan with asingle relief valve, which separatereliefvalves would then be adjusted to provide different hydraulic back pressures in accordance with the areas of their associated ends of the piston. However, the use of a single relief valve in the manner shown and described will be satisfactory in most cases.

After the various adjustments described above have been made, and with the`piston 254 and the various valves in the position` shown, the piston is raised at a relatively slow feed rate by providing an electrical signal which energizes the solenoid of the valve 36 to shift the valve stem 124 to the start position.` This causes the charging ilu'id from the gear pump 26 to be directed to the piston feed pump so that the feed pump begins to deliver the compressed hydraulic actuating fluid. This fluid is directed through4 the valves 38 and 40 and a conduit 222 tothe lower end of the cylinder in' the manner described above for shifting or actuating the piston upwardly. The hydraulic fluid in the upper endy of the cylinder is returned'to theY reservoir through the valve 40 and the relief valve 52 and is maintained in a compressed state under pressure by the relief valve in the manner and for the purpose described above. After the piston has been raised the desired amount, it is stopped, and in accordance with another important feature of the present invention the piston is stopped with great precision. YFor example, the piston may be stopped within .00001 (one hundred-thousandth) of an inch or less. The stopping of the piston is accomplished by shifting the valve stem'124 of the valve 36 back to the stop position, at which position the charging uid from the gear pumpis cut off from the piston `feed pump. When this occurs, the piston pump instantly stops de- Y livering the actuating fluid and the check valves in the piston pump prevent previouslydelivered fluid from flowing back into the piston chambers. Furthermore,`the check valve 46 prevents previously delivered tluid from returning Ifrom the uid motor, but since in this respect, the check valve 46 duplicates the function of the check valves in the piston pump, the check valve 46 could be K eliminated if-it were not for the rapid traverse circuit to be described below. When delivery of the actuating fluid from the feed pump is stopped, the back pressure in the liuid motor causes substantially instant stopping of the piston. Furthermore, it is important to note that this back pressure maintains the actuating fluid trapped in the iluid motor in a compressed state so that there will be substantially no shifting or actuation of the piston as would occurif the back pressure were eliminated and the actuating fluid were allowed to expand. It will be appreciated that any desired means may be provided for controlling the operation of the valve 36 and thereby controlling the operation of the iluid motor 32. However, by way of example, it may be stated thaty the solenoid of the valve 36 may be energized in response to a signal provided by a gauging device, not shown, checking a workpiece, and since the piston is actuated at a substantially uniform rate, a timer, not shown, may be provided for deenergizing the solenoid of the 4valve 36 after a predetermined ltime interval which corresponds to a predetermined amount of piston movement. As will be understood, when Vthe piston 254 is in the raised position it may be fed downwardly in they same manner that it was fed upwardly except, of course, that the vvalve 40 should be actuated to direct the uid from the feed pump to the upper end of the cylinder.

"Phe fluid motor 34 and the elements of the apparatus particularly associated with it are identical to the corresponding elements of the apparatus described above and, therefore, will not be set forth in detail. It suffices to state that the outlet port 172 of the valve 38 is connected with the inlet of the check valve 48 by a conduit 290 and the outlet of lthe check valve is connected withA an inlet port 292 of the valve 42 by a conduit 294.A Ports 296 and 2998V 'of thef'valve which Y*correspond to," the above. described ports 214'and 216 of the .valve 40 'are respectively connected with the lowerjandupper ends of the fluid motor`34 by conduits 300 and1302: Ports 304 and 306 of'the valve 42 which corresponds `with the above described ports 218 and 220 yare connected with the back pressure Yconduit 230 by conduits 308 and 310, .re-

spectively.. The Huid motor 34 is actuated at a feed rate 'in the same manner/as the fluid motor 32 except, of

course, that the' valve 3S is shifted to establish communicationl between i-ts inlet and outlet ports 162 and 172 and to block the inlet 162 fromthe outlet port 170.

lhydraulic fluid under pressure is discharged from the rapid traverse pump into an 'outlet conduit 322. The outlet conduitconnects with `an inlet port 324 of the manually adjustable'by-pass valve 54 and also with a conduit 326 which has branches 328, 330 and 332, respectively, communicating with ports 334, 336 and 338 of the valve 44. As shown in Figs. l and9, the valve structure 44 includes a body member 340 having a cen- ]tral bore 342 slidably ,receiving a valve stem` 344 and communicating with the inlet' .port 336.

In addition, a pair of outl'etrports .3 46jand 3:48 in the valvel body cornmunicate with axially spaced' portions of the bore. ,The

' valve stem is normally held in the position shownv in Fig.

9 so that the portv346 which is connected with the above described conduitV 204 is blocked and so that the `port 348V is also blocked, which port is connected with the above described conduit 294 by a conduit 350. Thus, the iluid entering the port 330 is blocked and the valve 54 which-will be described below functions to direct the fluid from th'e rapid traverse pump back to the reservoir. The valve stem 344 is resiliently held in the stop or neutral position shown by a spring 352 which surrounds a rod 354 connected with the -valve.stem. VThe spring acts against oppositely disposed collars 356 a-nd 358 slidably mounted on the rod and respectively confined for limited movement by a shoulder 360 formed on a cap member 362 and an abutment provided by an annular ring 364. Furthermore, the rod-is provided with an abutment in the` form of a nut 366 for cooperating with the collar 356 and an abutment in the form of a shoulder 368 for cooperating with the collar 358. When the valve stem is shifted toward the right as viewed in Fig. 9, it is seen that' the collar 356 will also shift toward the right so that the spring is compressed and will serve to return the valve stem to the neutral position. Also when the valve stem is shifted toward the left, the spring is compressed by the collar 358 and will serve to return the valve stern to the neutral position. The valve s-tem 344. is vactuated either toward the right or toward the Vleft by hydraulic uidunder pressure which flows from I 344 toward the right as viewed in Fig. 9 so that iiuid may flow from the inlet port 330 to the outlet port 346. -From the outletport, the fluidflowsl through the conduit 204 to the valve 40 from where it may'be selectively directed to either'end of the iluid motor. The check'l valv'e'46 'motion while the other uid I sageway 4l4also intersects the bore 404.

iseves `to prevent the now of rapidtraverse iiuid back lto the valve' 38. It should vbe noted that during vrapid -traverse of the piston 254, back pressure is maintained in the uid motor by the relief valve 52 in the manner described above and this enables the piston to be stopped in a precise manner after the rapid traverse movement has been completed. This is highly advantageous since the length of the feeding motion may be held to a miniand a total time required for a given movement of thepiston may be reduced. The nid motor 34l may lsimilarly be actuated by the rapid traverse pump merely by shifting the valve stem 344 toward the right as viewed to Vthe valve 38, the apparatus may be operated so that one of the iluid motors Vis Vbeing shifted with a feeding motor is being shifted with a apid traverse motion;`

[The manually adjustable by-pass vvalve 54 is shown v in detailin Fig. 8 and includes a body member-*380 hav- I ing a -bore 382 formed therein. The upper end ofthe bore is closed by a plug 384 and the lower end is closed "by an vauxiliary body member 386 having an outlet passageway 388 therein to which a drain conduit 390 is connected. A valve seat 392 is provided on 'the `auXiliary body member and a piston -394 is slidably mounted in -thebore 382`and is provided with a'reduced diameter valve portion 396 'adapted to Vengage the valve seat. The

piston lis yieldably biased by a spring 398 so as to urge the valve 396 against the valve seat. As will be understood,V vthe hydraulic'ud entering the inlet port 324 will be-blocked `bythe valve 396 until the pressure is raised -suicieiitly to force the piston upwardly against the ac- However, in'

f and adjusting a hydraulic back pressure in the upper end of the bore 382. This means includes a passageway 400 communicating with the lower end of the bore 382 and intersectinga passageway 402 and a bore 404. Fluid entering the passageway 402 is metered through a restricted orice 406 and then flows into a passageway 408. The passageway 408 is connected with the upper end of the bore 382 by a passageway 410 and it is also connected with the bore 404 bya passageway 412. A drain pas- A Valve stem 416 is slidably disposed in the bore 404and is resiliently biased to the position shown by a compression spring 418 which acts against a threaded plug 420. The threaded plug .420 is connected lto or made integral with a stem 422 projecting through a seal 424. Y A knob 426 is secured to the outer end of `the stem 422 so that .the position of the plug 420 may be easily manually adjusted-to adjust the pressure applied by the spring 418. With the f vstructure just described, hydraulic iluid flows from the lower portion of the bore 382 into the passageway 400 and a portion of this iiuid is metered and directed to the upper end of the piston 394 to aid the spring 398 in res isting opening of the valve 396. Another portion of the fluid flows into the lower end of thebore 404 and tends vto raise the valve stern 416 `against the action `of the spring relieves the lhydraulic yback pressure 'against 'the upper fend of thel piston 394 sothat the valve 396 is .permitted to 4open.4

. As shown in Fig. 3, there is a lsmall chamber atthe leftend ,of` the valve bore 210 into which a small amount o;f-`flu idmay leal( past the valve stem, and in order to diain' any fleakage fluid,- a drain port 430 is provided. :This drain port is connected with the reservoir -by con-1 .duits 432. 434, 436, 45s and 444o. The other above es scribed vdirectional control valves are'provided with-s lardrainports which are also connected With the reservoir. MoreV specifically, the valve 42 is provided with a drain port 442 which is connected tothe drain' conduit 434 by a conduit 444, the valve 38 is provided with'a drain port 446 which is connected with the drain conduit 434 by a conduit 448, the valve 44 is provided with a pair of drain ports 450 and 452 which are connected With-the drain conduit 440 by conduits 454 and 456, and the valve 36 is provided with a drain port 458 which is connected .with the drain conduit by a conduit 460.

In Fig. 11 there is shown an `apparatus 470 embodying a modified form of the present invention. Thiseinbodirnent of the apparatus includes a u-id vrnotor 4 72 comprising a cylinder 474 and a relatively slidable doubleacting piston 476 which is connected with a 4ra'rnl`478. The piston is formed so that there will lbe a predetermined amount of -frictional resistance to relative sliding motion between the piston and the cylinder. Thea'pparatus 470 also includes a gear pump 480' of known construction, a piston type feed 'pump 482 similar to the feed `pump described above, a directional control 'valve 4 484'simi1ar to the above described valve 36, a directional control valve 486 similar to the above described valve 40 yand a plurality of the relief valves 488, 490 and 492 similar to the above described vrelief valve 52.

- The inletl side of gear pump 480 is connected by a conduit 494 with a reservoir 496 and the compressed hydraulic fluid under pressure is discharged from Athe gear 'pump into a conduit 498. The conduit 498 is connected with the inlet of a lter 500 and the outlet of, the iil't'er assembly `is connected with an inlet port 502 of'the 'valve 510 is connected by conduits 512 and 514 with the inlet 516 ofthe. relief valve 490, and the outlet 51s of 'fue relief valve 490 is connected with the reservoir 496 by a conduit 520. The conduit 512 is also connected with a port 522 of the valve structure 484. 'Ihe valve struc ture 484 is. also provided with a port 524 which is connected with an Ainlet port 526 of 'the feedpump by ja conduit 528, and a port 530vwhich is connected with; ports 532 and y534 in the valve structure 486 by a conduit 536 and branch conduits 538 and "540, 'Ip'he valve st'r'ucture 48.4 is provided with a shiftable valve stem 542 which lmay be actuated by a solenoid 544V to and from ,St'art and stop positions. The valve stem 542 is constructed so that when it is in the stop position, the'A inlet port 502 is connected with the port 530 and these ports 'are blocked from the ports 522 and 524, and when the valve stem is in the start position, the port 502 is connected 'with the port 524 and communication is established between the ports 522 and 530. The valve structure 484 tis provided with a drain port 546 through which any leakage fluid `may pass into a drain line 548.

The piston Ytype vfeed pump 482 has an outlet 550 which is "connected by a conduit 552 with an inletport 554 of the valve structure 486. This conduit is .also connected by a branch conduit 556 with an inlet of the safety relief valve 492 which is normally closed and which functions to prevent injury to the apparatus. 4. The outlet of the relief valve 492 isconnected by a conduit 558 with the reservoir. The valve structure 486 isalso provided with ports 560 and 562 which are respectively connected with ports 564 and 566 in the lower and upper ends of the cylinder by conduits 568V and 570." The valve 4structure- 486 is provided with a valve stem l572.3 vhich may be actuated in oppositedrections by s lenoidsA 574 and 576. The valve stem 572 is formed` so that `when it is in the position shown, the 'portsn554 'and-560 are connected, the ports 532 and 562 are connected andfthe 'fof the relief valve 490'.' This sudden "low "11 `and v560 willbe connected, while the port 532 will be blocked. I'

The'operation of the apparatus 47,0is as'follows.

Starting with the position and the directional control'valve u stems in the positions shown, the gear and feed pumps A are continuously. driven by any suitable" means such as an electric motor, not shown. The hydraulic/huid delivered by the', gear pump is returned to th'ejre'servoir n and in the upper end of the fiuid motor is raised to about 50 p.s.i. since, 'as describedv above, the ports502v and 530 in the valve 484 are connected and the -ports `532 and 562 in the valve 486'are connected.Y However,.sirlce l the port` 524 inthe valveV 484 is blocked, no charging tluid is directed 4to the piston type feed pumpfsothat' the feed pump is not delivering any iiuid. Now, toinitiate upward feeding movement of the piston 476, the solenoid S44V is energized to 4shift the valve stem S42'to thelstartposition. When this occurs, theport 502fis connected with the port 524 sorthat charging fluid is delivered to `the feed pump and the feed pump Sbegins'delivering compressed hydraulic actuating fluid underhpressure which is directed by the Yvalve structureL 486' to the'- lower port 564 of the Huid motor. YAt the same tim ethe port530 ofnthe valve structure 484 is connected with the port 522 and thuskwith the relief valve 490 'so that lthe "back pressurein vthe upper end of the liuidj rnotor is,

instantaneouslyrv dropped to 'about the' pressurefsetting vvback pressure inthe uid 'motor facilitat `,'rapid; and 'A smooth starting ofthe pistonsince any .tendency for". the .piston to stick as a result of friction is 'subtsantially instantaneously overcome. However, it. shouldbe noted that the back pressure in the duid motor during'the feeding movement is still. sufficient to maintain the hydraulic actuating uid delivered by the feed pump .in a' compressed state so as to promote kuniform motion of the piston. Upward feeding movement of the piston may be stopped at anytime in a precise manner by 'merely ,shift- @ing the valve stem 542 back to itsstop position" so as to cut off the charging fluid from the feed pump. It is important to note that when the valve stem 542 is shifted back to the stop position, the back pressure in the. upper end of the fluid motor is substantially instantaneously .raised to approximately the same pressure as the actu- *ating Huid which is trapped between the lower end of the piston and the check valves in the piston type feed pump. Thus, the piston is stopped instantaneously and the trapped actuating hydraulicnuid is maintained in a compressed state, so that any further actuation ofthe piston is prevented. In accordance with rthe present invention, the friction between the piston and vcylinder n by shifting the -valve stem572 of the valve structure .486.

j However, as mentioned above in the description relating to the apparatus 20, the feeding 4motionis relatively slow. Iherefore, in many instances it is desirable totprovide the apparatus 470 with means for rapidly traversing the ,piston. downwardly. This may be accomplished by pro- 'viding the apparatus 470 witha manuallyoperatedgreset valve 590 which iscUnnectedto the portj564io-the K At the same time hydraulic fluid in the conduits 504, 536, 538, 570

the reset valve590includes a bodyv member 594 vhaving an kinlet port 596 connected wi-th the conduit`592 and intersectinga valve Ychamber 59S which hasone end 'closed by a plug 600. The body member is also provided with a central passageway 602 and a valve seat 604 between the Vvalve chamber and the passageway 602.' An outlet port 606 communicates with the passageway 602l andis connected with a drain line 60S. The aper- Nture through the' valve seat is normally closed by al ball `t'ype'valve memberl which is resiliently'biased against the seat by a spring 612 and which is also normally held against the seat by the hydraulic actuating fluid under pressure.Y Means is provided for manually shifting the valve member off the seat and this means includes astem 614 which projects through a sealing device 616 and hasV an enlarged threaded portion 618. The stem also is provided withla finger portion'm620 for engaging the ball valve withoutblocking thevalve. passageway so that when the stem is turned to thread Yitl further into the valve body, the ball valve is unseated and thevalve is opened.

.APreferably, a knob 622`is secured to the outer end of the Vstern to facilitate "turning thereof; When the valve 590 is opened, the uid in the lower end of the cylinder flows through the valve and back to the drain. lAt the same time, the fluid under pressuree in the upper end ofthe cylinder forces the piston down rapidly. e While the preferred embodiments of the present invention have been shownl and described herein, it is obvious motor, onetway conduitY means for delivering hydraulic .435 fluid under pressure'to` oneside of the shiftable element r`tially to eliminate movementv of the shiftable element as a result` of compression of the hydraulic uid, pump lmeans having a discharge connectedwith said one way conduit means and also connected with said -back presing uid from the pump means to said one way conduit 2. A hydraulic actuating apparatus comprising a fluid motor including a cylinder and a double-acting piston relatively slidably'disposed within this cylinder, one way conduit means for delivering hydraulic fluid underl pressure to one end of said cylinder relatively to shift said piston and cylinder, means including a back pressure valve connected by passageway means with an opposite end of said cylinder for providing a back pressure in said cylinder sucient substantially to eliminate relativemovement between the piston and cylinder as a result of compression of the hydraulic fluid, pump means having a discharge connected with said one way conduit means and also connected with said passageway means, and control valve means connected with said pump discharge selectively for directing fluid from said pump means to saidl one'way conduit means and to said passageway means. Y 4.

3. A hydraulicactuating apparatus comprising a uid motor, one way conduit means for metering hydraulic uid and for-delivering a`metered amount of hydraulic fluid under pressure to'one side of a relativelyshiftable -and expansion of the hydraulic fluid, pump means having a discharge connected withl saidy one way conduit `rneans andv also'with said back .pressure .providing means between said Huid motor and said back pressure providing means, and control valve means connectedl with said pump means discharge selectively for directing uid from said pump means to said one way conduit means and to said back pressure providing means.

`4. A hydraulic actuating apparatus providing a fluid motor, means for pressurizing and compressing hydraulic uid, means connected with said pressurizing means for metering the pressurized and compressed hydraulic fluid, one way conduit means for delivering the pressurized and compressed fluid to one side of a relatively shiftable element of the fluid motor, means connected' with Ysaid uid motor at an opposite side of said relatively shiftable element for providing a back pressure in said uid motor suficient to maintain said hydraulic fluid in a substantially uniform compressed state, and means including control valve means selectively for directing uid from said pressurizing and compressing means to said metering means and to said back pressure providing means.

5. A hydraulic actuating apparatus comprising a uid motor, one Way conduit means for delivering compressed hydraulic actuating fuid under pressure to said fluid motor, means providing a predetermined back pressure in said uid motor to maintain said hydraulic uid in a 'compressed state, said fluid motor being constructed so as to have a predetetrmined small frictional resistance to relative motion between parts thereof, which frictional resistance is utilized in combination with said back pressure to maintain the hydraulic uid in a compressed state so as to permit variation in the back pressure, pump means having a discharge connected with said one way conduit means and also connected with said back pressure providing means between the back pressure providing means and said fluid motor, and control valve means connected with said pumpimeans discharge selectively for directing fluid from the pump meansy to said one Yway conduit means and to said back pressure providing means.

6. A hydraulic actuating apparatus comprising a pair of fluid motors, one way conduit means includingffeed pump means for delivering compressed hydraulic actuating fluid under pressure, charging pump means for delivering fluid in a compressed state and under pressure to said feed pump means, means for selectively connecting said feed pump means with said uid motors, rapid traverse ypump means, means for selectively connecting said rapid traverse pump means with said uid motors, means for preventing hydraulic uid lfrom said rapid traverse pump means from entering the uid motors when the uid motors are connected with the feed pump means, valve means connected by passageway means with said fluid motors for providing a predetermined back pressure in y said uid motors to maintain the hydraulic uid from the feed pump means in a compressed state, conduit means connecting said passageway'means and said charging' pump, and control valve means connected with said charging pump and said conduit means selectively for 'directing iiuid to said feed pump for causing the feed pump ,to deliver actuating fluid and for directingv uid 14 to said passageway, means for stopping delivery of actu ating hydraulic uid from the feed pump means and for maintaining the backipressure and for maintaining the hydraulic fiuid previously delivered to the fluid motors from the feed pump means in a compressed state substantially to eliminate any further actuation of the motors.

7. A hydraulic actuating apparatus comprising a uid motor, pump means for delivering compressed hydraulic fluid under pressure, a first relief valve connected with said pump means, a second relief valve connected in series with said first relief valve, means connected, with said pump means for selectively `delivering compressed hydraulic actuating uid to said fiuid motor and for stopping delivery of the actuating fluid to the uid motor while maintaining previously delivered actuating fluid in a compressed state, and means for connecting both of said relief valves in series with said fluid motor when delivery of actuating uid is stopped for providing sufiicient back pressure to prevent actuation of the uid motor and for connecting only said second relief valve to said fluid motor when actuating uid is being delivered to the uid motor for providing a reduced back pressure to permit actuation of the fluid motor.

8. A hydraulic actuating apparatus comprising a fluid motor, pump means for delivering compressed hydraulic -uid under pressure, relief valve means including first and second portions associated with said pump means for establishing a first predetermined back pressure, said second relief valve means portion being operable independently of said first portion for establishing a second back pressure substantially lower than said first predetermined back pressure, means connected with said pump means for selectively delivering compressed hydraulic actuating fluid to said fiuid motor and for stopping de livery of said actuating fluid to the Huid motor while y maintaining previously delivered actuating uid in a com- References Cited in thev file of this patent UNITED STATES PATENTS 2,005,731 Ernst June 25, 1935 2,024,251 Romaine Dec. 17, 1935 2,345,973l Harrington Apr. 14, 1944 2,493,828 vParsons Jan. 10, 1950 2,497,608 Herrstrum et a1. Feb. 14, 1950 2,589,204 Parsons 1 Mar. 11, 1952 2,605,707 Worlidge Aug. 5, 1952 2,656,445 Svenson Oct. 20, 1953 

